This invention relates to a level meter that employs the radar principle and serves to measure the fill level of a medium in a container, as well as to a signal transmitter for transmitting an electromagnetic signal, an electric conductor system for conducting the electromagnetic signal into the container and returning reflected components of the electromagnetic signal from the container, and a signal receiver for receiving the reflected components of the electromagnetic signal, with the upper end of the electric conductor system featuring a suspension by which it is attached to a device on the container.
The measuring process of a level meter that employs the radar principle and incorporates an electric conductor system for conducting an electromagnetic signal into and back from the container is based on the time domain reflectometry (TDR) principle applied, for instance, in cable testing and resembles the mode of functional operation of conventional radar systems. In a TDR level meter of this type, for instance, an extremely short electric pulse is transmitted, via an essentially straight conductor system, into a container holding a medium such as a liquid, a powder, or a granular substance whose level is to be measured. Such an electric conductor system typically extends into the medium and is designed as a single-conductor or a dual-conductor assembly.
The short pulse, fed into and guided by an appropriate electric conductor system, travels into the container where it is at least partly reflected back by the surface of the medium, and the reflected component of the short electric pulse is collected by the signal receiver, allowing the determination of its runtime and thus of the level of the medium in the container. The reflected component of the short electric pulse depends on the dielectric constant of the medium and increases with the latter. The runtime of the signal is proportional to the height of the level of the medium in the container. Varying ambient conditions such as a rising or falling atmospheric pressure or rising or falling temperatures do not affect the measuring accuracy of the TDR level meter. Moreover, the runtime of the signal remains unaffected by the dielectric constant of the medium whose level is to be measured.
TDR level meters are occasionally employed in the measurement of the level of liquids a substantial distance away, as well as in granular bulk-material applications. It is especially in granular substance applications that the medium adheres to the conductor system or that process-related movement of the liquid within the container results in major mechanical tensile forces bearing on the conductor system and thus on its suspension. This can damage the conductor system and its suspension.